// Copyright (c) 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// Given a starting render_process_id and main_render_frame_id, the
// WebContentsTracker tracks changes to the active RenderFrameHost tree during
// the lifetime of a WebContents instance. This is used to maintain capture of
// the WebContents's video and audio across page transitions such as user
// navigations, crashes, iframes, etc..
//
// Threading issues: Start(), Stop() and the ChangeCallback must be invoked on
// the same thread. This can be any thread, and the decision is locked-in once
// WebContentsTracker::Start() is called.

#ifndef CONTENT_BROWSER_MEDIA_CAPTURE_WEB_CONTENTS_TRACKER_H_
#define CONTENT_BROWSER_MEDIA_CAPTURE_WEB_CONTENTS_TRACKER_H_

#include "base/callback.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "content/common/content_export.h"
#include "content/public/browser/web_contents_observer.h"

namespace base {
class SingleThreadTaskRunner;
}

namespace content {

class RenderWidgetHostView;

class CONTENT_EXPORT WebContentsTracker
    : public base::RefCountedThreadSafe<WebContentsTracker>,
      public WebContentsObserver {
public:
    // If |track_fullscreen_rwhv| is true, the ChangeCallback will be run when a
    // WebContents shows/destroys a fullscreen RenderWidgetHostView. If false,
    // fullscreen events are ignored. Normally, specify true for video capture and
    // false for audio capture.
    explicit WebContentsTracker(bool track_fullscreen_rwhv);

    // Callback to indicate a new RenderWidgetHostView should be targeted for
    // capture. This is also invoked with false to indicate tracking will not
    // continue (i.e., the WebContents instance was not found or has been
    // destroyed).
    typedef base::Callback<void(bool was_still_tracking)> ChangeCallback;

    // Start tracking.  The last-known |render_process_id| and
    // |main_render_frame_id| are provided, and |callback| will be run once to
    // indicate whether tracking successfully started (this may occur during the
    // invocation of Start(), or in the future).  The callback will be invoked on
    // the same thread calling Start().
    virtual void Start(int render_process_id, int main_render_frame_id,
        const ChangeCallback& callback);

    // Stop tracking.  Once this method returns, the callback is guaranteed not to
    // be invoked again.
    virtual void Stop();

    // Returns true if this tracker is still able to continue tracking changes.
    // This must only be called on the UI BrowserThread.
    bool is_still_tracking() const { return !!web_contents(); }

    // Current target view. May return nullptr during certain transient periods.
    // This must only be called on the UI BrowserThread.
    RenderWidgetHostView* GetTargetView() const;

    // Set a callback that is run whenever the main frame of the WebContents is
    // resized.  This method must be called on the same thread that calls
    // Start()/Stop(), and |callback| will be run on that same thread.  Calling
    // the Stop() method guarantees the callback will never be invoked again.
    void SetResizeChangeCallback(const base::Closure& callback);

protected:
    friend class base::RefCountedThreadSafe<WebContentsTracker>;
    ~WebContentsTracker() override;

private:
    // Determine the target RenderWidgetHostView and, if different from that last
    // reported, runs the ChangeCallback on the appropriate thread. If
    // |force_callback_run| is true, the ChangeCallback is run even if the
    // RenderWidgetHostView has not changed.
    void OnPossibleTargetChange(bool force_callback_run);

    // Called on the thread that Start()/Stop() are called on.  Checks whether the
    // callback is still valid and, if so, runs it.
    void MaybeDoCallback(bool was_still_tracking);

    // Called on the thread that Start()/Stop() are called on.  Checks whether the
    // callback is still valid and, if so, runs it to indicate the main frame has
    // changed in size.
    void MaybeDoResizeCallback();

    // Look-up the current WebContents instance associated with the given
    // |render_process_id| and |main_render_frame_id| and begin observing it.
    void StartObservingWebContents(int render_process_id,
        int main_render_frame_id);

    // WebContentsObserver overrides: These events indicate that the view of the
    // main frame may have changed.
    void RenderFrameCreated(RenderFrameHost* render_frame_host) final;
    void RenderFrameDeleted(RenderFrameHost* render_frame_host) final;
    void RenderFrameHostChanged(RenderFrameHost* old_host,
        RenderFrameHost* new_host) final;

    // WebContentsObserver override to notify the client that the source size has
    // changed.
    void MainFrameWasResized(bool width_changed) final;

    // WebContentsObserver override to notify the client that the capture target
    // has been permanently lost.
    void WebContentsDestroyed() final;

    // WebContentsObserver overrides to notify the client that the capture target
    // may have changed due to a separate fullscreen widget shown/destroyed.
    void DidShowFullscreenWidget() final;
    void DidDestroyFullscreenWidget() final;

    // If true, the client is interested in the showing/destruction of fullscreen
    // RenderWidgetHostViews.
    const bool track_fullscreen_rwhv_;

    // Pointer to the RenderWidgetHostView provided in the last run of
    // |callback_|. This is used to eliminate duplicate callback runs.
    RenderWidgetHostView* last_target_view_;

    // TaskRunner corresponding to the thread that called Start().
    scoped_refptr<base::SingleThreadTaskRunner> task_runner_;

    // Callback to run when the target RenderWidgetHostView has changed.
    ChangeCallback callback_;

    // Callback to run when the target RenderWidgetHostView has resized.
    base::Closure resize_callback_;

    DISALLOW_COPY_AND_ASSIGN(WebContentsTracker);
};

} // namespace content

#endif // CONTENT_BROWSER_MEDIA_CAPTURE_WEB_CONTENTS_TRACKER_H_
